On Mon, Apr 1, 2019 at 7:51 AM Liran Alon <liran.alon@xxxxxxxxxx> wrote:
>
> Ping.
>
> > On 25 Mar 2019, at 21:09, Liran Alon <liran.alon@xxxxxxxxxx> wrote:
> >
> > Issue was discovered when running kvm-unit-tests on KVM running as L1 on
> > top of Hyper-V.
> >
> > When vmx_instruction_intercept unit-test attempts to run RDPMC to test
> > RDPMC-exiting, it is intercepted by L1 KVM which it's EXIT_REASON_RDPMC
> > handler raise #GP because vCPU exposed by Hyper-V doesn't support PMU.
> > Instead of unit-test expectation to be reflected with EXIT_REASON_RDPMC.
> >
> > The reason vmx_instruction_intercept unit-test attempts to run RDPMC
> > even though Hyper-V doesn't support PMU is because L1 expose to L2
> > support for RDPMC-exiting. Which is reasonable to assume that is
> > supported only in case CPU supports PMU to being with.
> >
> > Above issue can easily be simulated by modifying
> > vmx_instruction_intercept config in x86/unittests.cfg to run QEMU with
> > "-cpu host,+vmx,-pmu" and run unit-test.
> >
> > To handle issue, change KVM to expose RDPMC-exiting only when guest
> > supports PMU.
> >
> > Reported-by: Saar Amar <saaramar@xxxxxxxxxxxxx>
> > Reviewed-by: Mihai Carabas <mihai.carabas@xxxxxxxxxx>
> > Signed-off-by: Liran Alon <liran.alon@xxxxxxxxxx>
> > ---
> > arch/x86/kvm/vmx/vmx.c | 25 +++++++++++++++++++++++++
> > 1 file changed, 25 insertions(+)
> >
> > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> > index f6915f10e584..2634ee8c9dc8 100644
> > --- a/arch/x86/kvm/vmx/vmx.c
> > +++ b/arch/x86/kvm/vmx/vmx.c
> > @@ -6978,6 +6978,30 @@ static void nested_vmx_entry_exit_ctls_update(struct kvm_vcpu *vcpu)
> > }
> > }
> >
> > +static bool guest_cpuid_has_pmu(struct kvm_vcpu *vcpu)
> > +{
> > + struct kvm_cpuid_entry2 *entry;
> > + union cpuid10_eax eax;
> > +
> > + entry = kvm_find_cpuid_entry(vcpu, 0xa, 0);
> > + if (!entry)
> > + return false;
> > +
> > + eax.full = entry->eax;
> > + return (eax.split.version_id > 0);
> > +}
> > +
> > +static void nested_vmx_procbased_ctls_update(struct kvm_vcpu *vcpu)
> > +{
> > + struct vcpu_vmx *vmx = to_vmx(vcpu);
> > + bool pmu_enabled = guest_cpuid_has_pmu(vcpu);
> > +
> > + if (pmu_enabled)
> > + vmx->nested.msrs.procbased_ctls_high |= CPU_BASED_RDPMC_EXITING;
Doesn't this require that L0 supports RDPMC exiting, so that the bit
can be passed from vmcs12 to vmcs02?
> > + else
> > + vmx->nested.msrs.procbased_ctls_high &= ~CPU_BASED_RDPMC_EXITING;
> > +}
> > +
> > static void update_intel_pt_cfg(struct kvm_vcpu *vcpu)
> > {
> > struct vcpu_vmx *vmx = to_vmx(vcpu);
> > @@ -7066,6 +7090,7 @@ static void vmx_cpuid_update(struct kvm_vcpu *vcpu)
> > if (nested_vmx_allowed(vcpu)) {
> > nested_vmx_cr_fixed1_bits_update(vcpu);
> > nested_vmx_entry_exit_ctls_update(vcpu);
> > + nested_vmx_procbased_ctls_update(vcpu);
> > }
> >
> > if (boot_cpu_has(X86_FEATURE_INTEL_PT) &&
> > --
> > 2.20.1
> >
>
